In the case of volatile compounds, the addition of a solvent with relatively low dielectric properties can be used to ensure that the solvent temperature is kept lower to cool off the solutes once they are liberated into the solvent [ 7 ] . Generally, hexane is used for the extraction of volatile oils [ 13 ] . In addition, the solvent-free MAE (SFMAE) process has been designed for aromatic herbs rich in volatile oils; in this case, the moisture content within the plant matrix itself serves for extraction and no solvent is used [ 29, 31 ] .
Studies have reported that ethanol or water can be added into poor microwave absorbers, such as hexane, to improve the extraction ef fi ciency. One of the most used solvent mixtures is hexane-acetone [ 8 ] , and only a small amount of water (about 10%) must be added in nonpolar solvents such as hexane, xylene, or toluene to improve the heating rate [ 8 ] . Zhou and Lui [ 32 ] evaluated different mixtures of ethanol and hexane in the extraction of solanesol from tobacco leaves; the 1:3 ratio gave the best yield. Comparing isopropanol and hexane for rice bran oil extraction,